1. Field of the Invention
The present invention relates to a toner for use in electrophotographic image formation, and to a method for preparing the toner. In addition, the present invention relates to a developer, an image forming method and an image forming apparatus using the toner.
2. Description of the Related Art
Various researches and developments have been made for electrophotography. Electrophotographic image forming methods typically include the following processes:
(1) Charging an image bearing member such as a photoreceptor (Charging process);
(2) Irradiating the image bearing member with light to form an electrostatic latent image on the image bearing member (irradiating process);
(2) Developing the electrostatic latent image with a developer including a toner to form a toner image on the image bearing member (developing process);
(3) Transferring the toner image onto a recording material such as paper sheets (transferring process); and
(4) Fixing the toner image on the recording material upon application of heat and pressure or the like thereto, resulting in formation of an output image (fixing process).
Contact heat fixing methods such as heat roller fixing methods have been typically used for the fixing process. Fixing devices for use in the heat roller fixing methods include a heat roller and a pressure roller, and a recording material bearing a toner image is fed through a nip between the heat roller and the pressure roller so that the toner image is melted and fixed on the recording material.
It is preferable for the toner used for developing electrostatic latent images to include a polyester resin, which has an advantage in fixing property, and to have a spherical form while having a particle diameter of about few micrometers and a sharp particle diameter distribution so as to produce high definition images.
In order to prepare such a preferable toner, solution suspension methods, in which toner components such as a binder resin (e.g., polyester), a colorant and a release agent are dissolved or dispersed in an organic solvent to prepare a toner component liquid (i.e., oil phase liquid), and the toner component liquid is dispersed in an aqueous medium to prepare a colored particulate material (i.e., toner particles), and emulsion association methods, in which particulate toner components such as a particulate resin (e.g., particulate polyester), a particulate colorant and a particulate release agent are aggregated in the presence of a flocculating salt or the like, followed by a reshaping treatment to prepare a colored particulate material have been proposed.
In order to prepare a colored particulate material having a sharp particle diameter distribution using the solution suspension methods, techniques such that a fine particulate resin is dispersed in an aqueous medium to stably disperse a toner component liquid in the aqueous medium have been proposed. Specifically, there is a proposal for a technique in that a resin solution serving as an oil phase liquid is dispersed in an aqueous medium, in which a fine particulate resin is dispersed, to prepare a particulate resin having a sharp particle diameter distribution.
However, the toner preparation methods for stably dispersing an oil phase liquid in an aqueous phase liquid using a fine particulate resin have a drawback such that the dispersing conditions of the oil phase liquid in the aqueous medium change depending on the properties of such a fine particulate resin such as particle diameter and zeta potential. In other words, the properties of the fine particulate resin have to be severely controlled to control the conditions of the oil phase liquid dispersed in the aqueous medium. Therefore, it is difficult for the toner preparation methods to stably produce a desired toner.
For these reasons, the present inventors recognized that there is a need for a solution suspension method by which a particulate material (such as toner) having desired properties can be stably produced.